A circuit arrangement having a substantially corresponding operating principle is for example known from German Auslegeschrift No. 2,050,994. It operates in such a manner that at the testing point, a transmitter is fed with high-frequency oscillations, whereby this transmitter is converted to a damped condition on a first transfer coil by an arriving d.c. signal through a circuit element on one side of the testing point, which damped condition is evaluated through a second transfer coil for characterizing the d.c. signal on the other side of the testing point. A third transfer coil serves to feed the transmitter from a high-frequency generator. The d.c. signal is characterized by the control of a transistor with the half-waves of high-frequency oscillations, which half-waves appear at the second transfer coil. The transistor is thus converted to a defined switching condition during the signal duration, which condition can be evaluated as a signal.
A further known possibility for transmitting of d.c. signals lies in the use of a transmitter, which transmits the on and off operations of the d.c. signals and thus permits impulselike signal simulations. However, to overcome signal distortions which occur requires a high amount of circuit components.
Further, it is possible to feed a transmitter for transmitting d.c. signals from a special generator having high-frequency oscillations which, corresponding with the d.c. signals, are controlled on the primary side and deliver on the secondary side after rectification again a d.c. signal which corresponds to the supplied d.c. signal. However, in such circuits, due to the preoscillation condition of the high-frequency generator in connection with the transmitter, the transmitting speeds are held within relatively low limits. To increase the transmitting speed, it is also possible to provide accelerating circuits, which improve the preoscillation condition of a generator, however, also increase the expense of the circuit.
From German Auslegeschrift No. 1,244,242 an arrangement for transmitting d.c. signals is known, which operates with a feed-back generator and transforms impulse combinations into square-wave currents or sinusoidal currents, whereby also a rectification after transformation is used. This arrangement operates with a transmitter, in which high-frequency oscillations are produced with the aid of an amplifier and in which a control occurs on the primary side by the d.c. signals, so that on the secondary side after rectification of the oscillations again a d.c. signal is available. The d.c. signal effects thereby on the primary side through a different damping a use or nonuse of the oscillations.
The known possibilities for the ungrounded transmission of signals through testing points have the common disadvantages of a required additional generator with associated current supply, of a limited transmitting speed and of only a limited possibility of analogue reproduction of the signal behind the testig points. Further, a special voltage is always required, which is controlled, so as to speak, through the criteria transmitted through the testing point for the signal reproduction.
The purpose of the invention is to design a circuit arrangement, through which the transmission of analogue or digital signals through testing points is possible with the least possible input and without additional generators having associated current supplies operating at a high transmitting speed to effect an as exact as possible signal reproduction without requiring a special voltage to be switched.
A circuit arrangement of the above-mentioned type is constructed to attain this purpose such that an oscillator feeds a rectifier circuit and is operated in dependency of the signal polarity by the high-frequency oscillations in the inductive coupling and in power adjustment with respect to a load resistor which is adjusted corresponding to the signals to be reproduced.
A circuit arrangement of this type thus operates in such a manner that the inductors of an oscillator define the transmitter at the testing point. This oscillator is operated with the voltage of the signals to be transmitted through the testing point and is not just only controlled. A special coil of the transmitter being part of the oscillator is used for removing the oscillations produced by the generator during each signal. If these oscillations are now rectified and the thereby obtained d.c. current is fed to a load resistor and charging capacitor, then a signal drop occurs which corresponds to the wave form of the input signals, because their amplitude determines the amplitude of the respectively produced oscillations. It is thus possible, to transmit analogue and digital voltage signals through a circuit arrangement of the invention.
The output adjustment of the oscillator to the load resistor is necessary in order to assure, in view of the low signal voltages, an as high as possible output. Same may reach values, which lie at approximately 80%. Furthermore the adjustment to the load resistor brings about a high damping, which favors the preoscillation and decaying behavior of the oscillator. The entire circuit arrangement having a small toroidal core for the oscillator can be stored within a volume of approximately 20 .times. 10 .times. 10 mm., this size represents an optimum compared with other components of the signal transmitting technique. It is for example possible to install the circuit into an apparatus plug.
A circuit arrangement of the invention permits, depending on the selection of the high-frequency signal, transmitting speeds of up to 9600 Bd. which corresponds to an oscillating frequency of approximately 1 MHz. This results also from the fact that the circuit arrangement is operated, and not controlled by, the signal voltages themselves and that preoscillation difficulties of the oscillator circuit must not be feared, because a special transmitter with high inductors does not exist and all components of the oscillator may be high-frequency structural parts. To assure a high efficiency and high oscillation amplitudes, the oscillator is built advantageously with a high LC-relationship.
The circuit arrangement of the invention can, due to the fact that the signal voltage is used as the operating voltage for the oscillator, with only one oscillator transmit naturally only signals of a pregiven polarity. If double current signals having an alternating current direction are to be transmitted, then according to a further development of the invention, two oscillators are required, the first inductors of which are associated with different polarities of the input signals and the output coupling coils of which are connected each through a rectifier to a common load resistor.
It is possible with such a circuit arrangement to operate the two input circuits alternately with the signals of the one or of the other polarity. The respectively associated oscillator becomes then effective and produces a high-frequency oscillation, which after rectification results on the secondary side in a direct voltage. By suitably coupling the load resistors, the double current signals can again be produced in a circuit.
A circuit arrangement of the above-mentioned type is advantageously further constructed in such a manner that the first inductors of the oscillators are arranged in similarly constructed circuits which function in response to different current-directions and are connected parallel with one another. Thus, it is possible to provide one single signal input, whereby depending on the polarity of the signals either the one or the other oscillator is switched to become effective.
The circuit arrangement for double current signals can be constructed very advantageously such that each rectifier is connected in series on one side with a coil end of the respective output coupling coil, on the other side with the emitter-collector path of a transistor and that a load resistor which is common to both rectifiers is connected at the connecting points of the one transistor with the other coil end of the other output coupling coil.
In this circuit arrangement the direct voltages obtained from the respective rectification are connected at a common load resistor, namely so that the transistor connected at the outlet side of the respective rectifier and the free coil end of the respective output coupling coil form outputs, which are connected in parallel with the outputs of the respective other, similar arrangement. This type of connection of the positive and the negative signal components at a simultaneous optimum power adjustment between the two oscillators and the common load resistor leads to a further reduction of the circuit expense, which would be created if one would connect the two signal components on the secondary side in a different manner. The transistors, which are connected at the outlet side of the rectifiers, function as valves and prevent the respective negative or positive voltage which occurs at the common load resistor from being short-circuited through the respective other rectifier in the described parallel connection.